Re: [stable 5.10 PATCH] mm: khugepaged: skip huge page collapse for special files

On Wed, Nov 03, 2021 at 01:22:58PM -0700, Yang Shi wrote:

commit a4aeaa06d45e90f9b279f0b09de84bd00006e733 upstream.

The read-only THP for filesystems will collapse THP for files opened readonly and mapped with VM_EXEC. The intended usecase is to avoid TLB misses for large text segments. But it doesn't restrict the file types so a THP could be collapsed for a non-regular file, for example, block device, if it is opened readonly and mapped with EXEC permission. This may cause bugs, like [1] and [2].

This is definitely not the intended usecase, so just collapse THP for regular files in order to close the attack surface.

[shy828301@gmail.com: fix vm_file check [3]]

Now queued up, thanks.

greg k-h